The role of tissue nitrogen content in growth allocation within Spartina alterniflora L

Growth allocation to green leaves, stems, roots, rhizomes, and rhizome tip tillers of Spartina alterniflora under low nitrogen conditions was investigated in a hydroponic greenhouse experiment. The critical nitrogen content (CNC) needed in various tissues to maintain basic metabolic functions was determined while the role of tissue nitrogen content on growth allocation was investigated. The general pattern of all tissues showed an increase over time; this increase was coupled with a decrease in tissue nitrogen content. When the external nitrogen was depleted, the growth of the green leaves ceased first, quickly followed by the growth of the other tissues. The leaf CNC (0.052 +/- 0.005 g N/g C) was not significantly different from that of the rhizome tip tillers (0.050 +/- 0.003 g N/g C), but was significantly higher than that of the stems (0.031 +/- 0.002 g N/g C), roots (0.033 +/- 0.001 g N/g C), rhizomes (0.031 +/- 0.005 g N/g C), and the nitrogen content of senesced leaves (0.030 +/- 0.002 g N/g C). After leaf CNC was reached, leaf senescence increased dramatically. Rhizome tip tillers and rhizomes received most of their photosynthates after reaching leaf CNC.